>>718215203
Yeah, ranked runs aren't for everyone.
For a casual playthrough you really can ignore the arena and you'll be fine. Or you can just approach it conservatively to avoid wasting time. You face the same opponents for every character, with a couple changes for melee vs ranged. Sigurd will clear easily, the other units can safely kill the first couple of enemies, and then stop.
Even if some of your guys lose in the arena and begin the chapter with 1hp it's no problem, it's arguably even a good thing because your healers can get exp from healing them during the first couple of turns where you're moving toward the enemy.
If you have a unit with wrath you can activate it by losing in the arena.
If you want to train a weak unit and you don't want to use the arena you still have options. You can transfer gold with your thief, you can allow some enemies commanders to return to their castles and bring out extra reinforcements (= infinite grinding), you can rescue civilians with your weak unit to level up.